Rebuilding 3ym30 - Timing mystery

[Woodyv12]

In process of rebuilding my 3ym30 after broken conrod.
All good so far..but puzzled by white paint marks on idler gear .
The white marks are from factory, why are they there,
and why do they not coincide with instructions in re-assembly diagram?
Even diagram leaves out info on A on Crankshaft gear

"B" letter lines up with paint mark as does the "C" but..
"A" doesn't ..the paint and letter don't line up...which should I follow?

Anybody with some knowledge?

[coopec43]

Maybe something here? Don't get it wrong!!!

3YM30/3YM20/2YM15 - J/109 Class
https://j109.org/docs/yanmar_3ym-2ym-service-manual.pdf
Apr 25, 2005 - (3YM30,. 3YM20). 1. Front cover added to engine outline. 2. ... Model 3YM30 has been used for the illustrations in this service manual, but they apply to other models in ...... 5.7.2 Gear timing marks. ... 5.8 Flywheel and housing ...

3YM30/3YM20/2YM15 M E101 - PDF - DocPlayer.net
https://docplayer.net/60128176-3ym30...15-m-e101.html
3YM30/3YM20/2YM15 M E101 Manual Name Engine Model: Number of revision ... oil in the combustion chamber during the operation, and white smoke, oil hummer .... Injection timing marks T.D.C. Valve clearance Flywheel d) Adjusting other ..


Yanmar 3YM20 valve clearance - myHanse - Hanse Yachts Owners Forum ...
www.myhanse.com › General › Chit Chat
Nov 11, 2011 - 10 posts - ‎6 authors
White hull, tiller, short keel and rudder, standard North sails, Sparcraft rig ... We have a 3YM30 engine from 2005 and I believe we have used it 450 .... the flywheel marks were really easy to see and the whole process was ...

Timing Gear; Inspecting The Gears; Gear Timing Marks - Yanmar ...
https://www.manualslib.com › ... › Engine › 3YM30 › Sevice manual
Yanmar 3YM30 Manual Online: Timing Gear, Inspecting The Gears, Gear Timing Marks. The Timing Gear Is Helical Type For Minimum Noise And Specially ..

Clive

[jimbunyard]

When you say 'rebuilding', do you mean complete disassembly and reassembly including geartrain?

The reason I ask is if the idler gear is not the same size as the cam and pump gears, after a single spin of the crank the marks won't line back up for a certain number of revolutions.

The service manual,

https://www.google.com/search?source....6.xfcIEfBqsKI

seems unambiguous on the matter, the 'a's, b's and c's' should line up initially.

Unless I had a good reason to do otherwise, I'd follow the service manual and not the painted marks.

[Compass790]

With our engine its line up the letters. I'd ignore the paint IMO. How did your conrod break? Curious to hear if you know what caused it. I welded one up ( NOT RECOMMENDED) as they wanted $630 for a new one.

[RaymondR]

Probably just dabbed on the highlight the stamped marking whereabouts.

[Woodyv12]

Thanks guys,

Yes, complete strip and reassemble,
Worked out that the gears "walk" and don't mesh in the same position as they rotate..apparently to minimise harmonics and wear..very cleaver. I will ignore paint marks as I can find nothing to indicate that it is a factory adjustment or such.

I do not know why the conrod broke, there was no water in cylinder and correct oil levels.
The boat is in Charter and I wasn't present when it happened. Interestingly the engine ran more or less OK when idling. The crank bearing was stuffed but cylinder bore escaped unmarked as rod broke about in two places so nothing was left to damage sides.

[Compass790]

thanks for update. Very lucky it didn't destroy the sleeve. Pity you couldnt find a reason for the fractures. How much Yanmar gunna ream ya for the conrod?

[Woodyv12]

Didn't ask Yanmar the cost..would be a stupid price.
I obtained complete piston/conrod as well as crank shaft for $Au 600 from a Yanmar dealer who had spares from a motor with similar problem. Sent the lot to my engine builder (does our race cars) for checking, honing and assembly of pistons/crank.

My preferred option would have been to just replace the engine but Yanmar has upgraded 3ym30 so new motor torque/speed would not have matched old motor. Couldn't find a similar s/h motor and didn't feel like stumping up for two new motors so we now have a new learning experience. Expect to complete process for around 2.5k